I would recommend Across The Wide Missouri by Bernard Devoto. If you can, find an old hardback because it has the wonderful picture plates. Here is an excerpt from a 1947 review talking about the plates: > >The most striking and satisfying features of the book are its eighty-one fine plates, nineteen of them in color. Most of the plates are reproductions of spot water-color sketches and paintings made by Alfred Jacob Miller, the artist employed by Sir William Drummond Stewart to accompany him into the Rocky Mountains in 1837 and 1838. Since the British sportsman and officer lived and traveled with the fur brigades, Miller had opportunity to paint the only known pictures actually made among the Rocky Mountain trappers of that era. So far as we know, his were also the first paintings made of scenery along the trail to Oregon. Mrs. Clyde (Mae Reed) Porter of Kansas City discovered a hundred of Miller’s sketches...